In the construction of highway bridges extending over land or water and of the type including steel and/or concrete girders, it is necessary to position and later remove, forms used for supporting concrete poured between two adjacent girders (and along the outside edges of each outermost girder), during the formation of the bridge deck (which will eventually support the traveling surface of the bridge). When the concrete cures, thus forming the bridge deck, the metal or wooden forms which are used to support the poured concrete (hereafter called "forms") are removed from below, typically being lowered onto a barge or truck using a winch or crane.
Several devices have been developed to assist in the placement and removal of the forms. U.S. Pat. No. 2,639,950 issued to Wheeler, for example, discloses a device which includes a travelling derrick assembly having a scaffold which is supported below the bridge girders. The scaffold is assembled on and supported by two parallel beams extending across the width of the bridge. Each end of the two beams hangs from a travelling derrick which operates along the completed bridge road surface. Several winches and cranes are used to separate and manipulate the two beams around obstructions, such as the supporting pilings, encountered as the entire device moves along the length of the bridge.
Although the device of U.S. Pat. No. 2,639,950 could be used to assist in lifting forms to a position lying just below the bridge girders, the device still requires workmen to lift and assemble each lifted form into a locked and supporting position between two girders. Furthermore, the procedure required to prevent the scaffold from hitting obstacles, such as pillars, is awkward, slow and includes several dangerous steps.